I just found this 2010
Trek Soho for 350 bucks. It was a steal (I think). I have a nice road bike, but was looking for a commuter to go 7-20 miles roundtrip depending on my job for the day/week (I work on two different campuses). If you are diligent, you can certainly find a good deal. If you can find the bike, or bikes you want, set up an RSS feed so you can hop on it as soon as it comes up.
What do you want besides just a bike that can go a mile to the beach? Want an upright, comfortable bike? Have to carry it up any stairs? Need gears or is it flat enough terrain for a single speed? Do you want to do as little maintenance as possible on the thing?
Your local bike shop should have something simple and in your price range if you don't want to go through the craigslist hassle though.